Apparatus for transporting sample holders

ABSTRACT

Apparatus for transporting elongated sample holders in a sample holder storage compartment past an operating station at which sample tubes contained in the sample holders may be removed and then returned to the sample holders. First and second parallel conveyors on opposite sides of the operating station drive the holders toward and away from the operating station. A lateral drive system engages the holders in longitudinal stop positions at opposite ends of the conveyors and drives them laterally between the conveyors to lateral stop positions, one of the holders during lateral movement being driven into and away from an operative position at the operating station. Encoded labels are displayed on each sample holder for indicating the incremental spacing between the sample tubes carried in the sample holder. Detectors are provided for reading the encoded labels and convey a signal in accordance with the labels to a control system which controls the operation of the first and second conveyors and of the lateral drive system.

BACKGROUND OF THE INVENTION

The present invention relates to sample transport apparatus and, moreparticularly, to apparatus for circulating sample holders and in astorage compartment past and operating station.

A prior art sample transport apparatus was disclosed in U.S. Pat. No.3,859,528 issued to Luitwieler Jr. et al., issued Jan. 7, 1975 andassigned to Beckman Instruments, Inc., the assignee of the presentinvention. The prior art apparatus is designed for circulating aplurality of sample holder vials past an operating station. The vialsare supported within respective compartments of multi-compartment sampleholding trays which are circulated in rectilinear fashion in the samplestorage compartment of the apparatus.

An elevator is provided at the operating station for removing a vialfrom the sample tray and positioning it in a radiation detection chamberfor analysis, and then returning the vial to the sample tray in thecompartment. A plurality of sample trays are contained in the storagecompartment and grouped in two longitudinally extending, generallyparallel columns on opposite sides of the operating station.Longitudinally movable fingers at opposite ends of each column move theentire column of trays incrementally, in a longitudinal direction, adistance of one tray depth to drive trays in the first column toward theoperating station and trays in the second column away from the operatingstation. After moving each column of trays longitudinally, trays at theremote ends of the columns are indexed laterally from one column to theother after which the fingers again move the columns in increments ofone tray depth.

Although the foregoing apparatus adequately performs its intendedfunction, it does not possess certain advantages for which there iscurrently a demand. For example, as a result of the limited longitudinaldrive capabilities of the incrementing fingers, incremental movement ofeach tray column requires that each tray abut an adjoining tray so thatthe trays can push each other serially in domino fashion.

The consequence of this arrangement is that unless the apparatuscontains a full load of trays, the incrementing fingers will be unableto move the tray columns longitudinally to positions whereby the traysat the remote ends of the columns can be laterally indexed betweencolumns. Also, when indexing, the apparatus may fail to accurately aligna tray in position over the elevator at the operating station. In such acase, instead of engaging and removing the sample vial, the elevatorwill instead strike the tray and may jam the apparatus. In addition,there is no provision in the prior apparatus for detecting andcorrecting malfunctions of this kind.

There is, accordingly, need for sample transport apparatus havingbroader capabilities than those of the prior art. There is, for example,a need for apparatus which is capable of circulating sample holders ofany number ranging from one to a full load and whereby a plurality ofsample holder types, each adapted for carrying sample tubes of differingsize and number can be freely mixed; and whereby jam-ups or stoppages ofthe transport apparatus are automatically detected and corrected.

SUMMARY OF THE INVENTION

The present invention provides apparatus for transporting elongatedsample holders past an operating station in a sample holder storagecompartment. Each sample holder is adapted to contain a row of sampletubes of uniform size. The sample holders may include a plurality oftypes, however, wherein each type is characterized by the size of thesample tube it is adapted to contain and the incremental spacingprovided therebetween.

The various sample holder types have in common a registration surface ona first elongated side spaced a predetermined distance from the centerline of the sample tubes. A horizontal groove extends the length of thesecond elongated side of each sample holder.

A first continuous conveyor means is provided on one side of theoperating station for conveying the sample holders positioned thereon ina first longitudinal direction toward the operating station. Guide meansadjacent one end of the first conveyor means are provided to halt thelongitudinal motion of sample holders in the first longitudinaldirection, and to define a first longitudinal stop position for eachsample holder. The first longitudinal stop position is located adjacentthe operating station.

Lateral drive means engage each sample holder in the first longitudinalstop position and move it laterally along the guide means into and thenaway from an operative position at the operating station. The lateraldrive means include a continuous roller chain disposed generally aboutthe periphery of the storage compartment. Means are provided forsupporting and driving the chain, which has a path of travel alongsidethe first longitudinal stop position and past the operating station. Aplurality of dogs are mounted to the chain for engaging and drivingsample holders when the sample holders are in the first longitudinalstop position.

In accordance with another aspect of the invention, encoded label meansare displayed on each sample holder for indicating the incrementalspacing between the sample tubes carried in the sample holder. Also,detector means are mounted on the sample holder storage compartmentahead of the operating station for reading the encoded label means. Theoutput signal of the detector means is indicative of the incrementalspacing between the sample tubes carried in the sample holder. Controlmeans are provided for receiving a signal from the detector means andcausing the lateral drive means to move the sample holder in accordancewith the signal. The lateral drive means, thereby, automaticallyposition, in turn, each sample tube of the sample holder in an operativeposition at the operating station.

In accordance with further aspects of the invention, contact means areprovided for engaging and stabilizing each sample holder while it is inthe first longitudinal stop position. The contact means cause the sampleholder to abut the guide means and resist any upward motion that may beimparted to the sample holder by the operating station when the sampleholder is in an operative position.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the transport apparatus of theinvention.

FIG. 2 is a fragmentary top view with a cover removed to show a portionof a chain drive included in the apparatus of FIG. 1.

FIGS. 3 and 4 are partial perspective views of a sample holder employedin the practice of the invention.

FIG. 5 is an elevation view of the sample holder of FIGS. 3 and 4.

FIG. 6 is a fragmentary perspective view of a sample holder in anoperating position with the apparatus of FIG. 1.

FIGS. 7 and 8 are end views of two types of sample holders, each adaptedto hold sample tubes of a given size.

FIG. 9 is a simplified block diagram of a control means for thetransport apparatus of FIG. 1.

DETAILED DESCRIPTION

In FIG. 1 there is shown a storage compartment and sample transportapparatus as employed in systems such as a radiation measuring analyzer.Reference numeral 10 designates the storage compartment which isgenerally rectangular and adapted for supporting a plurality of sampleholders 12. The sample holders are circulated along a rectilinear pathpast an operating station 14.

In accordance with one important aspect of the present invention, thesample transport apparatus is designed to circulate along a rectilinearpath any desired number of sample holders 12 from one up to a full load.To accomplish this, the sample transport apparatus includes a first andsecond parallel conveying means which engage and drive the sampleholders in first and second opposite directions toward and away from theoperating station 14.

The first conveying means includes a pair of conveyor belts 30 on whichthe sample holders 12 are supported for horizontal movement in thedirection of the arrow toward the operating station 14. The secondconveyor means includes a second pair of conveyor belts 32, generallyparallel to belts 30, on which sample holders 12 are supported forhorizontal movement in the opposite direction away from the operatingstation 14. The two conveyors 30 and 32 thus frictionally engage anddrive sample holders 12 in opposite longitudinal directions in ahorizontal plane.

First and second guide means 36 (only one of which is shown and is bestillustrated in FIGS. 1 and 6), are provided adjacent opposite ends ofthe first and second conveyor means for halting the motion of sampleholders in the first and second directions, respectively, and to definefirst and second longitudinal stop positions for each sample holder. Thefirst sample holders on the first and second conveyors therefore aredriven until arriving at first and second longitudinal stop positions atthe end of the respective conveyors.

After the first sample holder on the conveyor 30 arrives at the firstlongitudinal stop position, it is stepped laterally by lateral drivemeans between the conveyors 30 and 32 past the operating station 14.During such stepping motion, each sample tube 16 contained in sampleholder 12 is positioned in turn at the operating station 14 foranalysis. While this is taking place, a sample holder positioned on thesecond conveyor means will have reached the second longitudinal stopposition and will be stepped laterally in synchronism with the movementof the first sample holder past the operating station.

At the end of such lateral movement, the sample holders occupy first andsecond lateral stop positions on the conveyors 32 and 30, respectively,which once again transport the sample holders in a longitudinaldirection. Thus, rectilinear circulation of sample holders in acounterclockise direction along and between the two conveyors continuesduring operation of the sample transport apparatus 10.

It should be noted that although rotation of sample holders along acounterclockwise path is the normal mode of operation for the apparatusdescribed, the apparatus is fully capable of operation in the reversedirection for the purpose of repeating operation on one or more selectedsample holders. Also, it should be noted that operation may be carriedout with any number of sample holders 12 ranging from one to a fullload. In this regard, a full load is the maximum number of sampleholders that can be positioned on each conveyor 30 and 32 minus twolarge or three small type sample holders on each conveyor to allow forshifting of holders between conveyors.

By way of further description of the sample transport apparatus ofsample storage compartment 10, the conveyor belts 30 of the firstconveyor means are driven by a pair of motor driven pulleys 54 and passaround a piar of idler pulleys 56 at opposite ends thereof. Similarly,belts 32 of the second conveyor means are driven by motor driven pulleys58 and pass around respective idler pulleys 60 at their opposite ends. Apair of bidirectional motors (not shown) are each connected to thedriving pulleys 54 and 58, respectively, to power the first and secondconveyor means independently of each other. In this arrangement, thebelts slide over the top surface of the sample compartment base 9 andthe belts 30 are driven in the first longitudinal direction while thebelts 32 are driven in a second and opposite longitudinal direction.

In the center of the storage compartment base 9 is an elongated centerdivider 8, disposed longitudinally, and positioned between and generallyparallel to the conveyors 30 and 32. The center divider includes alongitudinal slot 7 on one elongated side, and a sensor housing 6mounted at the end adjacent the operating station 14. The sensor housing6 contains photooptical means (not shown in detail) for detecting thepresence of a sample tube 18 in each of the compartments 16 of sampleholder 12 when it is in an operative position at the operating station14.

The perimeter of the sample holder storage compartment 10 is bounded byvertical sides having overhanging top members 61 which enclose a drivechain 34 thereunder. First and second guide means 36 (see FIG. 1 andFIGS. 6-8 are provided adjacent the first and second longitudinal stoppositions, respectively. The first and second guide means 36 comprise alow ridge or shoulder which extends vertically from the storagecompartment base 9. The first and second guide means 36 halt the motionof sample holders in the first and second directions, respectively, andprovide a surface against which the sample holders are abutted whiletraveling in a lateral direction.

Located adjacent the outward sides of conveyors 30 and 32 are third andfourth guide means 62, respectively. Only one of these, the fourth guidemeans, is shown (FIG. 1). The third and fourth guide means comprise avertical shoulder extending upward of storage compartment base 9. Aguide slot 59 is defined by the space between the top of the fourthguide means 62 and the overhanging top member 61.

The third and fourth guide means 62 halt the lateral motion of sampleholders 12 traveling between conveyors 30 and 32. By so doing, the thirdand fourth guide means define respective first and second lateral stoppositions for each sample holder 12 when it is on conveyors 30 and 32.

Referring now also to FIG. 2, the lateral drive means which provides thestepping motion previously described will be explained in detail. Thelateral drive means comprise a continuous roller drive chain 34 disposedgenerally about the periphery of the storage compartment base 9. Thedrive chain 34 is supported by a plurality of sprockets 35. One sprocket35 is mounted at each point at which the chain changes direction and onesprocket 35 is mounted on stepper motor 39 which supplies the motivepower to the drive chain 34. A plurality of dogs 42 are mounted on thechain at spaced intervals for engaging and driving sample holders 12when the sample holders are in the first and second longitudinal stoppositions.

In another important aspect of the invention, the hinged plate 50 uponwhich stepper motor 39 is mounted, is hinged to storage compartment base9 through hinge pin 51. A spring 52 exerts an outward force on plate 50and thereby maintains tension on drive chain 34. The position of hingedplate 50 is sensed by switch 53 mounted on storage compartment base 9and connected to control means controlling the action of stepper motor39. When the drive chain tension on either side of stepper motor 39increases sufficiently to overcome the resisting force of spring 52, thecontinued rotation of the stepper motor causes the hinged plate 50 topivot in the direction of the storage compartment base 9, therebyactuating switch 53. Switch 53 is connected to control means whichinclude a microprocessor and which causes the stepper motor 39 toreverse its rotation for a specified time. By virtue of thisarrangement, jam-ups or stoppages in the lateral drive system such asmight be caused by a mispositioned sample holder are sensed andautomatically corrected.

Turning now to FIGS. 3-5 there is shown a suitable sample holder 12.Sample holder 12 has a generally rectangular base 13 supporting a row oftube compartments 16, each of which is adapted to receive and support asample tube 18. A horizontal groove 24 is provided along one side of thesample holder base 13 and a tab 17 is provided at the left end of thesample holder 12 with respect to the side having horizontal groove 24(FIG. 3).

When the sample holder 12 is being conveyed longitudinally to the firstlongitudinal stop position, tab 17 rides in longitudinal slot 7 incenter divider 8 as shown in FIG. 1. Tab 17 in cooperation withlongitudinal slot 7 serves to keep the sample holder 12 upright duringthe course of said travel. Similarly, when the sample holder 12 is beingconveyed in the opposite direction (toward the second longitudinal stopposition), tab 17 rides in the guide slot 59 formed by the fourth guidemeans 62.

Referring now specifically to FIGS. 4 and 5, attention is directed tothe opposite side of sample holder 12 wherein there are provided twolabel holders 40 and 41 for holding label means 44 and 45. Label means44 and 45 contain indicia which in conjunction with label detector means63 (FIG. 1) convey information to the control means for controlling theoperation of the sample transport apparatus. This aspect of theinvention will be further described herein elsewhere. Attention is alsodirected to the drive slot 47 of sample holder 12 which is adapted forreceiving and engaging a dog 42 of drive chain 34.

When a sample holder 12 arrives in the first longitudinal stop position,its longitudinal motion is halted upon abutting the guide means 36. Thesample holder remains in this position for a few seconds, until one ofthe dogs 42 of lateral drive chain 34 reaches the sample holder andengages its drive slot 47. During this brief waiting time, the belts (ofthe first conveyor means 30) upon which the sample holder is positioned,continue running in slipping engagement with the sample holder, whichserves to keep the sample holder in abutting contact with the guidemeans 36. Upon engaging the sample holder 12, the lateral drive meansmoves it laterally, so that the first compartment 16 is at the operatingstation 14.

Referring now to FIG. 6 and more particularly to the sample holder 12shown therein, it will be seen that sample tube 18 is disposed incompartment 16 and rests on the floor 20 thereof. The floor 20 of eachcompartment 16 includes a circular opening 22 which is of smallerdiameter than the sample tube 18. While the sample holder 12 is at theoperating station 13, the lateral drive means positions each compartment16 of sample holder 12 in an operating position. While in such position,circular opening 22 is in general alignment with the aperture 15 in thestorage compartment base 9.

As previously discussed, the apparatus of the invention is suited foruse in analytical instrumentation wherein it is required that eachsample tube be, in turn, extracted from the sample holder, analyzed inan analytical chamber, and then returned to the sample holder. Toaccomplish this, an elevator system having an upwardly moving elevatorrod is typically employed and well known in the art.

As employed by the apparatus of the invention, an elevator rod (notshown) extends upwardly through aperture 15 of storage compartment base9. The elevator rod passes through circular opening 22 of sample holder12 and lifts sample tube 18 out of its compartment 16 and into ananalytical chamber (not shown). When the analytical operation iscompleted, the elevator rod lowers to return the sample tube 18 to itsrespective compartment 16, whereupon the lateral drive means positionsthe next compartment in the operating position and the sequence isrepeated.

Referring now to FIGS. 6-8 the sample holder 12 is shown at operatingstation 14. The center divider 8 is disposed generally in line withoperating station 14, and at the end adjacent thereto is provided afirst contact member 5 for engaging and stabilizing sample holders 12 inthe first longitudinal stop position. The first contact member 5 isconfigured for engaging the horizontal groove 24 of the sample holder 12in sliding engagement therewith. This arrangement enables the sampleholder to be driven laterally, while engaged with the first contactmember 5. The first contact member 5 is spring loaded by spring means(not shown) which enables it to impart a force to the sample holder 12,causing it to closely abut the guide means 36 and maintain engagementwith dog 42 of the lateral drive means. In addition to this, the firstcontact member 5 functions as a "hold down" to prevent the sample holder12 from lifting if, through minor misalignment, it is contacted by theupwardly traveling elevator of the operating station 14.

In the preferred form, the horizontal groove 24 of sample holder 12 andthe contact member 5 have mating "V" configurations. However, otherconfigurations such as a rectangular tongue-in-groove configuration mayalso be used. The "hold down" capability of the first contact member 5is not required at the second longitudinal stop position, as there is noelevator at this location. Accordingly, the second contact member 4located adjacent this location is configured for simply bearing againstthe sample holder base 13 to ensure that the sample holder remainsengaged with the dog 42 of the lateral drive means.

Turning now to FIGS. 7 and 8, another important aspect of the inventionwill be described. As shown in the partial end views in which extraneousdetail in omitted, sample holders 12a and 12b contain sample tubes 18aand 18b, respectively. The sample holders are each shown engaged withfirst contact member 5, and in abutting contact with guide means 36. Forthe purpose of discussion, the portion of the sample holder abuttingguide means 36 is designated as reference surface 2.

Now, by noting that diameter "a" of sample tube 18a is markedly largerthan diameter "b" of sample tube 18b, it will be readily apparent thatsample holders 12a and 12b represent distinguishable types, wherein eachtype is adapted to contain a particular size sample tube. Since it isdesirable for the operation of the transport apparatus that the overalllength of sample holders remain constant, the number of sample tubes andthe incremental spacing between the tubes contained in any given sampleholder type is therefore a function of the tube diameter. Similarly, thewidth of various sample holder types must also vary according to thetube diameter.

A number of provisions incorporated by the invention enables thetransport apparatus to accommodate various sample holder types in anyorder or mixtures thereof, automatically. First, it will be seen thatalthough the upper portion of the sample holder type designated 12a islarger than that of 12b, the base portions of both types are identical.More specifically, the dimension marked "X" which is the distancebetween the tube center line and reference surface 2 is the same forboth holder types. Thus, in the longitudinal direction, the alignment ofthe respective holder types is assured.

As previously stated, the lateral positioning of sample holders atoperating station 14 is carried out by the lateral drive means. Theoperation of the lateral drive means, in turn, is governed by controlmeans which include a microprocessor and a plurality of detector meanswhich feed information to the microprocessor. More specifically, eachsample holder is provided with means for carrying label means 44 and 45,respectively, as shown by FIGS. 4 and 5. The label means are suitablyencoded, as by means of alternating black and white indicia appearingthereon, to display information pertaining to the sample holder type,identity, contents and selected program options. The label means 44 and45 are scanned by label detector means 63 (FIG. 1) which are mountedproximate guide means 36 at the first longitudinal stop position.

Label detector means 63 comprise an array of photo-optical detectorssuitable for reading binary coded indicia and the like. However, ifdesired, other label means and other methods of encoding and detectingsame may be employed. For example, the labeling means could bemagnetically encoded and read by suitable magnetically responsivedetectors.

Referring now to the block diagram of FIG. 9, the major functions of thecontrol means with regard to the operation of the sample transportapparatus will be described. When a sample holder 12 arrives at thefirst longitudinal stop position, label means 44 and 45 are "read" bylabel detector means 63, which provide signals to the microprocessor 66portion of the control means. Included in these signals is informationas to the sample holder type. This information enables the control meansto cause the stepper motor 39 to advance the correct number of steps toposition the first and succeeding compartments 16 of the sample holder12 in operating position at the operating station 14.

A sensor may be optionally employed in the sensor housing 6 to detectmissing sample tubes in a partially filled holder in order that theoperating sequence applied to the vacant stations be omitted. Inaddition, the information transmitted by the label detector means 63includes the identity of the specific sample holder and enables thecontrol means to implement specific options in the operating oranalytical process.

Other inputs to the microprocessor 66 include a signal from switch 53which detects jam-ups in the transfer apparatus by an increase in chaintension. Upon receiving such indication, the control means causes thefirst and second longitudinal drive motors 67 and 68, respectively, toalternately reverse directions in conjunction with reversing the steppermotor 39, to correct the jam-up.

Another input to the microprocessor 66 is from the dog sensors 69 whichwill be discussed, initially, in general terms. The precisionregistration of sample holders at the operating station is the result ofthe microprocessor causing the stepper motor to step the exact number ofsteps required for each movement of the sample holder. It is, therefore,necessary for the microprocessor to "know" the step-distance between theoperating station and the next approaching dog. If the transportapparatus traveled only in one direction, it would be a simple matter toestablish this distance as a fixed mechanical relationship.Bidirectional travel, however, introduces backlash error, making itnecessary to provide means for establishing the step-location of a dogas it approaches the operating station.

As the drive chain is of fixed length, and the seven dogs mountedthereon are spaced equally apart, the position of all dogs can beestablished upon fixing the position of one. Accordingly, first andsecond dog sensors 69, one of which is shown by FIG. 1, are located oneon each side of the operating station 14 at a point which may besubstantially removed therefrom. The first dog sensor 69 is used fordetecting the passage of dogs 42 traveling in the forward direction, andthe second dog sensor (not shown) is used for detecting the passage ofdogs traveling in the reverse direction. Thus, by detecting the presenceof a dog 42 at, say, the first dog sensor 69, which is a knownstep-distance from the operating station, the position of any dogintermediate the sensor and the station is determinable, since thedistance between dogs is also a known constant.

When the sample holder 12 arrives at the operating station 14, the firstcompartment of the sample holder 12 is positioned in the operatingposition. Upon completion of the operating cycle, the microprocessor 66causes the stepper motor 39 to step an additional number of steps, inaccordance with the sample holder type, to position the next compartment16 in operating position. The process is repeated, so that eachcompartment 16 is sequentially positioned at the operating station. Aspreviously discussed, the operating cycle may be skipped forcompartments not containing a sample tube 18, by use of optional tubedetector 6. When the sample holder 12 has completed its operating cycleat the operating station 14, the lateral drive means transports it tothe first lateral stop position, and the next following sample holder ismoved into operating position.

While in accordance with the patent statutes there has been describedwhat at present is considered to be the preferred embodiment of theinvention, it will be understood by those skilled in the art thatvarious changes and modifications may be made therein without departingfrom the invention and it is, therefore, the aim of the appended claimsto cover all such changes and modifications as fall within the truespirit and scope of the invention.

What is claimed is:
 1. Apparatus for transporting elongated sampleholders past an operating station in a sample holder storagecompartment, wherein each sample holder is adapted to contain a row ofsample tubes of uniform size and wherein said sample holders may includea plurality of types, each type characterized by the size of the sampletubes the sample holder is adapted to contain and the incrementalspacing provided therebetween, and each type having in common aregistration surface on a first elongated side spaced a predetermineddistance from the center line of said sample tubes, and a horizontalgroove extending the length of the second elongated side; said apparatuscomprising:a first continuous conveyor means on one side of saidoperating station for conveying sample holders positioned thereon in afirst longitudinal direction toward said station; first guide meansadjacent one end of said first conveyor means for halting the motion ofsample holders in said first longitudinal direction, and to define afirst longitudinal stop position for each sample holder; said firstlongitudinal stop position situated adjacent said operating station;lateral drive means for engaging each sample holder in said firstlongitudinal stop position and for moving said sample holders laterallyalong said guide means into and then away from an operative position atsaid operating station; said lateral drive means including a continuousroller chain disposed generally about the periphery of said storagecompartment; means for supporting and driving said chain; said chainhaving a path of travel alongside said first longitudinal stop positionand past said operating station; a plurality of dogs mounted to saidchain for engaging and driving sample holders when said sample holdersare in said first longitudinal stop position; encoded label meansdisplayed on each sample holder for indicating the incremental spacingbetween the sample tubes carried in the respective sample holder;detector means mounted on said sample holder storage compartment aheadof said operating station for reading said encoded label means, saiddetector means having an output signal indicative of the incrementalspacing between the sample tubes carried in the respective sampleholder; and control means for receiving said signal from said detectormeans and causing said lateral drive means to move the respective sampleholder in accordance with said signal and thereby automaticallyposition, in turn, each sample tube of the sample holder in an operativeposition at the operating station.
 2. The apparatus of claim 1 furtherincluding:first contact means for engaging and stabilizing each sampleholder while at said operating station, said contact means including acenter divider disposed generally in the center of said sample holderstorage compartment and extending longitudinally alongside said firstconveyor means; a contact member slidably mounted at the end of saidcenter divider adjacent said operating station; said contact memberspring loaded in the direction of said operating station; said contactmember configured for engagement and sliding contact with saidhorizontal groove extending the length of said second elongated side ofsaid sample holder for causing said sample holder to abut said guidemeans while at said operating station and for preventing upward movementof said sample holder.
 3. The apparatus of claim 2 wherein said meansfor supporting and driving said chain comprise:a plurality of idlersprockets mounted about the general periphery of said storagecompartment; a stepper motor; a sprocket mounted on the output shaft ofsaid stepper motor for driving said chain; said stepper motor mounted ona plate hinged to the periphery of said storage compartment; a springacting on said plate in a direction imparting tension to said chain;means for controlling the operation of said stepper motor.
 4. Theapparatus of claim 3 further including means for automatically reversingthe direction of said chain when it encounters abnormal resistance toits travel comprising:a swich mounted on one of said plate or saidstorage compartment so as to be actuated by rotation of said plate onits hinge; said switch when actuated providing a reversing signal tosaid means controlling the operation of said stepper motor.
 5. Theapparatus defined by claim 1 further comprising:a second continuousconveyor means disposed opposite said one side of said operating stationfor conveying sample holders positioned thereon in a second longitudinaldirection away from said operating station; second guide means adjacentone end of said second conveyor means opposite said one end of saidfirst conveyor means for halting the motion of sample holders in saidsecond direction and to define a second longitudinal stop position foreach sample holder.
 6. The apparatus of claim 5 further including secondcontact means adjacent said second longitudinal stop position forkeeping said sample holder engaged with the chain dog of said lateraldrive means.
 7. Apparatus for circulating sample holders along arectilinear path, past an operating station in a sample holder storagecompartment, each sample holder being adapted to contain a row of sampletubes, said sample holders having in common a registration surface on afirst elongated side and a horizontal groove extending the length of asecond elongated side; said apparatus comprising:first and secondparallel conveyor means disposed on opposite sides of said operatingstation for engaging and conveying sample holders positioned thereon infirst and second opposite longitudinal directions toward and away fromsaid operating station; motor means for driving said first and secondconveyor means; guide means adjacent each end of said first and secondconveyor means for halting the motion of sample holders in said firstand second longitudinal directions, respectively, and to define firstand second longitudinal stop positions for each sample holder; saidfirst longitudinal stop position situated adjacent said operatingstation; lateral drive means for engaging each sample holder in saidfirst and second longitudinal stop positions and for moving said sampleholders laterally along said guide means between said first and secondconveyor means, said lateral drive means moving said sample holder intoand then away from an operative position at said operating station whensaid sample holder reaches said first longitudinal stop position; saidlateral drive means including a continuous roller chain disposed aboutthe periphery of said storage compartment; means for supporting anddriving said chain; said chain having a circulating path of travelalongside said first and second longitudinal stop positions and pastsaid operating station; a plurality of dogs mounted to said chain forengaging and driving sample holders when said sample holders are in saidfirst and second longitudinal stop positions; encoded label meansdisplayed on each sample holder for indicating the incremental spacingbetween the sample tubes carried in the respective sample holder;detector means mounted on said sample holder storage compartment aheadof said operating station for reading said encoded label means, saiddetector means having an output signal indicative of the incrementalspacing between the sample tubes carried in the respective sampleholder; control means for receiving said signal from said detector meansand causing said lateral drive means to move the respective sampleholder in accordance with said signal and thereby automaticallyposition, in turn, each sample tube of the sample holder in an operativeposition at said operating station; and contact means for causing saidsample holder to abut said guide means and for preventing upwardmovement of said sample holder when at said operating station.
 8. Theapparatus of claim 7 wherein said contact means include:a center dividerextending longitudinally between said first and second conveyor means; acontact member slidably mounted at one end of said center divideradjacent said operating station; said contact member being spring loadedin the direction of said operating station and configured for slidablyengaging said horizontal groove of said sample holder, said contactmember applying a force to said sample holder causing it to abut saidguide means and said engagement of said contact member with saidhorizontal groove preventing lifting of said sample holder when saidsample holder is at said operating station.